The present invention relates to the field of fixed latency operations in time sensitive applications, such as setting a clock or determining latency, particularly in a downhole network along a drill string used in oil and gas exploration, or along the casings and other equipment used in oil and gas production.
Many modern processors, computers and embedded systems are interrupt driven systems, where the execution of a program may vary by more than one million cycles due to interruptions by the processor and other programs. In time sensitive operations such as setting a clock or determining the total latency of a network, interruptions and variable delays may cause inaccurate results. Several systems and apparatuses having specialized hardware for fixed latency operations are known in the art.
U.S. Pat. No. 6,073,053 discloses a reflex I/O card for an industrial controller to provide outputs at a fixed delay in time or portion of a machine cycle after the inputs through dedicated hardware thus avoiding transmission delays and processing delays associated with the communication of information to a central processor.
U.S. Pat. No. 6,654,834 discloses a method and apparatus for data transfer employing closed loop of memory nodes. Data transfer between a master node and plural memory nodes follows a synchronous fixed latency loop bus. This configuration provides a fixed latency between the issue of a read command and the return of the read data no matter which memory node is accessed.
U.S. Pat. No. 6,580,720 discloses a latency verification system within a multi-interface point-to-point switching system (MIPPSS). According to one aspect of the invention, the switching fabric provides a fixed, low latency signal path for each connection whereby the latency of that connection is deterministic and predictable. Moreover, the switching system ensures that the data content of the signal delivered via that connection is not analyzed by the switching fabric, i.e., the switching fabric operates in a message-independent manner.